I'm expecting delivery of a 8320 which is locked to Orange Uk soon.
I doubt it will have a sim with it, I was considering buying a £5 sim for PAYG and the calling Orange and asking if they will unlock it, has anybody done this?
I dont mind maying them of course.

Otherwise I will have to use one of the unlockers on the internet I guess?

Also once unlocked, will I need to do much to have it work with my T-Mobile UK data service?

i ain't from UK but i pretty much was in the same shoes you're in right now
i had my sister buy my 8320 at a shop right by queens, nyc late last year
then i purchased the unlock code from gsmphonesource.com (quick!)
then i had to have her let TMo release the PIN
and it has worked flawlessly since i got it
that's all there is that i could share